moved to newbie section...this is the best place for an answer to this, assuming by mp3 you mean car computer.
If mp3's are all your after having a port to plugin your mp3 player might be your best bet. Unless i'm mistaken in your motives.
There are also some stereos that will accept a usb device, so you can plugin a 500 gig usb hard drive that's been loaded with your music and be good to go. I believe kenwood makes one that has nav and video to boot.
I'll do the bumbling, and i'll be the idiot.
if you've got a "stupid" question, search for some of mine!